Sounds like you just need to replace the compressor. Just how did the contractor make your compressor go bad? I'm curious to hear that. The 13 minimum rating was in effect in 07. Manufacturers could not build anything smaller than 13 after that point. If you could find the equipment, you could install lower than that though. With an older coil and new unit, things CAN NOT be warranteed. Mixing the two is not a scam. If it were, I'd tell you. It doesn't affect my business any which way. Fact is things are made differently today as opposed to ten, twenty years ago. As far as installing yourself, and paying cash........ I'll give you a guess what happens if something goes wrong. No one will work on it under warrantee. Everything is contingent on install. Keeping the pump on it for HOURS is kind of useless also. Once the vacuum pulls down 29.5 lbs, guess what, there's no leaks. A little longer is'nt bad because it cleans the lines out. But as long as it's on for at least an hour your fine. 11 years isn't bad at all. You still have many years to go on that system. Just replace the compressor and you'll be fine. Just get a good company in there to do it. Call many companies and ask questions to find the right guys that's all.